Clinical quantitative flow cytometry is a new technology that utilizes specialized antibody staining techniques and fluorescent standards to quantitate antibody binding to different cell populations within a sample. The Flow Cytometry Unit uses this technique to quantitate tumor cell antibody binding capacity in patients undergoing various antibody based therapies. The flow cytometric assays are performed in place of previous studies using radioactively labeled antibodies. The flow cytometric assays are more rapid, make the use of radioactivity unnecessary and are performed on 100 uL of blood instead of 25mL. The data collected is also more precise and improves the ability of NCI investigators to compare antibody binding to tumor cells to treatment response. Quantitation of fluorescent antibody binding immediately post therapy also allows precise determination of saturation of antigen sites with non labeled therapeutic antibody. As the majority of NCI lymphoma and leukemia protocols include antibody based therapy in their regimens, this is a tremendous resource for NCI investigators. Antibody binding quantitation is not provided by reference laboratories.